Exemplary embodiments of the invention relate to a valve assembly, which can be arranged in a pipeline for liquid or gaseous media. In particular, the invention relates to a valve assembly, which can be actuated one time, for a space travel engine. The valve assembly comprises an inlet and an outlet, which open into a working chamber of the valve assembly, and an actuator. In a non-actuated state of the actuator, a flow passage between the inlet and outlet is blocked, which means that the valve assembly is closed.
Valves are used in general where, for example, a pipeline for liquid or gaseous media must be opened or closed. In the closed state of the valve, a very low leakage rate must be ensured through it. Depending on the application, the valves can be provided for multiple actuations or also only for single actuation, wherein the latter is the case, for example, in drive systems for space travel applications.
A valve used in a drive system for space travel applications is used in satellites or space probes, for example, for connecting a closed hydraulic or pneumatic system to its environment. Such a valve must be closed in a non-actuated (activated) state. This state is referred to as “normally closed” (NC). Propellant or gas lines of a drive system, for example, can thus be passivated or depressurized at the end of a mission.
High demands are placed on the reliability of the activation in the case of space travel applications, since a malfunction can cause great damage or even the loss of the drive system.
Exemplary embodiments of the present invention are directed to a structurally and/or functionally reliable valve assembly for opening or closing a valve and a corresponding drive system for space travel applications.
Exemplary embodiments of the present invention provide a valve assembly for one-time actuation, which can be arranged in a pipeline for liquid or gaseous media. In particular, the valve assembly can be used in space travel engines. The valve assembly comprises an inlet and an outlet, and also an actuator. The inlet and the outlet open into a working chamber of the valve assembly. In a non-actuated (activated) state of the actuator, a flow passage between the inlet and the outlet is blocked. This means that the valve assembly is closed when the actuator is not actuated. The actuator is a shape-memory actuator, which can be actuated one time, or comprises a shape-memory actuator, which suddenly changes its external shape upon reaching a conversion temperature, which is dependent on its alloy composition, and which can be generated by a controllable electrical heating device of the valve assembly. The actuator irreversibly destroys a pipe element, which separates the inlet from the outlet, in the working chamber upon actuation, whereby the inlet and the outlet are connected to one another with respect to flow via the working chamber.
In other words, the pipe element is arranged in the working chamber and is destroyed therein to open the valve assembly.
The use of a shape-memory actuator as or in an actuator enables the one-time and irreversible activation, i.e., opening, of the valve. The activation is performed in that the shape-memory actuator is heated by the energy which is externally supplied, i.e., from the heating device, whereby the actuator changes its size (i.e., for example, expands), in particular suddenly and thus mechanically destroys the pipe element which separates the inlet from the outlet. The mechanical destruction of the pipe element can be performed according to a first variant by shearing off or according to a second variant by tearing or breaking the pipe element.
With the actuation by supply of thermal energy, the shape-memory actuator returns into its original shape. The supply of thermal energy up to or beyond a so-called transition temperature enables, for example, an expansion of the actuator while providing greater forces (in the range of several kilonewtons).
For example, a nickel-titanium alloy (NiTi) can be used for the shape-memory actuator. A typical transition temperature in the case of such shape-memory actuators is approximately 70° C. to 80° C. For space travel applications, it is fundamentally advantageous if a material having a higher transition temperature, for example, between 100° C. and 120° C., is used. Unintentional triggering of the actuator as a result of unfavorable boundary conditions can thus be prevented more reliably. The higher transition temperature can be achieved, for example, by pre-stressing the actuator and by alloying refractory metals or metals from the platinum group with the NiTi alloy.
The actuation function of the actuator can be provided with high reliability. No further mechanical or pyrotechnic elements are required to actuate, i.e., open the valve, in addition to the (shape-memory) actuator and the heating device, whereby the valve assembly has a simple mechanical structure, which is therefore robust. The valve assembly may be produced using few components and can have a low weight.
As a result, the valve assembly is similar in its function to a pyrotechnic valve, but has simpler activation and longer shelf life in relation thereto. In addition, the valve assembly does not have losses due to leakage before the activation (actuation).
According to the first variant, the inlet opens into a pipe element, which is arranged in the working chamber such that the pipe element is sheared off upon the actuation (i.e., activation) of the shape-memory actuator, whereby the inlet and outlet are connected to one another with respect to flow via the working chamber. Alternatively, the outlet can open into the pipe element arranged in the working chamber such that the pipe element is sheared off upon the actuation of the shape-memory actuator.
In one embodiment of the valve assembly, the shape-memory actuator at least sectionally adjoins the pipe element in the non-actuated state, whereby the shape change of the shape-memory actuator results in shearing off of the pipe element by the shape-memory actuator itself. Before the actuation, the shape-memory actuator can press against the pipe element or can have a small distance to the pipe element, for example. The shape change executed by the shape-memory actuator upon the actuation then results in the desired shearing of the pipe element.
In another embodiment of the valve assembly, one or more intermediate parts at least sectionally adjoin the pipe element in the non-actuated state, so that the shape change of the shape-memory actuator is transmittable to the intermediate part or parts, whereby the pipe element can be sheared off by at least one of the intermediate parts. The shape change of the actuated shape-memory actuator is transmitted to other components, wherein then one of the components carries out the shearing of the pipe element. This variant enables greater degrees of freedom in the design of the actuator. Thus, for example, a force transmission can be implemented and/or the volume of the actuator can be optimized. The intermediate part can be implemented, for example, in the form of a valve piston.
The pipe element can be arranged in a longitudinal direction of the valve assembly, wherein the force that can be generated by the shape-memory actuator extends transversely to the longitudinal direction. This generates maximum shear forces upon the actuation of the shape-memory actuator, whereby the reliability of the shearing operation is optimized. “Transversely” means that the force extends in a plane which is approximately perpendicular to the longitudinal direction.
The pipe element can be arranged in a longitudinal direction of the valve assembly, wherein the force that can be generated by the shape-memory actuator extends in a rotating manner about an axis which extends transversely to the longitudinal direction. “Transversely” also means here that the force extends in a plane which is approximately perpendicular to the longitudinal direction. The shearing off is performed by a rotational movement of the shape-memory actuator or an optional intermediate part. The actuator can already be connected in a friction-locked and/or formfitting manner to the pipe element for this purpose before the actuation. The actuator can have a (small) distance to the pipe element in the non-actuated state.
The working chamber can comprise a receiving volume for the sheared-off parts of the pipe element. The receiving volume can be located outside a main flow path of the gaseous or liquid medium, so that parts which are sheared off by the actuation of the (shape-memory) actuator are not drawn in the direction of the outlet and do not clog it or reach the outside under certain circumstances.
The pipe element can be formed by a pocket borehole of the inlet, which is introduced from a side facing away from the working chamber into a terminal base of the inlet. This enables simple manufacturing. It enables the simple establishment of the forces required for the shearing by way of the wall thickness of the pipe element remaining after the creation of the pocket borehole.
The base and the actuator or the base and one or more of the intermediate parts can be spaced apart from one another in the longitudinal direction. This ensures that after the shearing operation the opening created at the inlet is not closed by the actuator. Depending on the actuator embodiment, the actuator or the intermediate part can also be provided adjoining the base. It must be ensured by the actuator embodiment here that after the shearing operation, the opening created at the inlet is not closed by an actuator component.
The shape-memory actuator can be a spring or a sleeve, for example, which expands upon reaching the conversion temperature. The spring or sleeve can drive a bolt or a similar part, for example, by which the shearing is caused.
In a second variant, the pipe element can be formed by an extension of the inlet or the outlet, wherein the pipe element has a material weakening extending around the circumference, in particular a groove or notch, in the working chamber, wherein the pipe element is torn or broken upon the actuation of the actuator by a force acting in the direction of the actuation. According to this embodiment, the pipe element is not destroyed by shearing, but rather by a force acting in the direction of the pipe element. One advantage of this variant is that a component of the pipe element does not have to be captured by or after the destruction. The receiving chamber can thus be designed more compactly. The valve assembly can thus be provided with smaller volume. The material weakening represents an intended breakpoint of the pipe element.
According to one embodiment, a longitudinal axis of the pipe element and a longitudinal axis of the actuator are arranged coaxially to one another. The pipe element and the actuator are therefore arranged “one behind the other” or one inside the other.
According to a further embodiment, the actuator is tubular and has in its interior one or more components for transmitting the movement executed by the actuator upon the actuation to the pipe element. The component(s) for transmitting the movement executed by the actuator upon the actuation comprise a shaft which, when the actuator is not actuated, represent an extension of the pipe element. The actuator is mechanically connected to the shaft for transmitting a force, to cause the destruction at the intended breakpoint of the pipe element upon actuation.
The following embodiments can be used in both variants.
A screen can be arranged in the working chamber (from the viewpoint of the working chamber) in front of the outlet or in front of the inlet (if the outlet opens into the pipe element). The throughput of the gaseous or liquid medium can be adjusted by the screen when the valve is open.
The pipe element can be monolithically connected to the inlet or the outlet (if the outlet opens into the pipe element). In this way, the valve assembly has excellent leak tightness before the actuation of the actuator. The leak tightness is always provided in this case independently from the length of a period of time until an activation of the actuator. The monolithic, i.e., one-piece implementation of inlet or outlet and pipe element enables a seal seat and a valve element movable in relation thereto to be omitted. The structure of the valve assembly can thus also be kept simple.
The pipe element can have a cross section that is smaller or at most equally as large as the inlet or the outlet (if the outlet opens into the pipe element). The forces required for the shearing off or tearing can be established, for example, by the ratio of the diameter of pipe element and inlet or outlet. The smaller the diameter of the pipe element in relation to the inlet or outlet, the lesser the shearing forces which are required.
Furthermore, a drive system for a space travel application is provided, which has at least one valve assembly of the above-described type. The drive system has the same advantages as were mentioned in conjunction with the above-described valve assembly.
In summary, the forces released by activation of a shape-memory actuator be used for destroying a pipe element to provide an (evacuation) valve which can be actuated one time.
The inventive valve assembly has an array of advantages:                The valve assembly has a low level of complexity.        The valve assembly can be provided having a low mass, which encourages the use in space travel applications.        The valve assembly has excellent leak tightness before actuation over an arbitrarily long period of time because of the design. This is enabled, for example, by the monolithically implemented inlet having the pipe element.        The valve assembly has a reliable function, which can be implemented in a manner designed for high-pressure applications by way of the dimensions of the pipe element (for example, in the form of a capillary pipe which is to be destroyed by shearing or by way of the embodiment of the intended breakpoint).        The valve assembly enables easy dimensioning ability for a required mass stream in the open state.        The valve assembly has a long service life, since a pyrotechnic charge having limited lifetime can be omitted. No induction of a pyrotechnic shock during the actuation of the valve assembly results in conjunction therewith.        Low demands are placed on control electronics, in particular no valve drivers or additional controllers are required.        Low demands exist on environmental conditions during the storage, in particular relaxed temperature demands in comparison to pyrotechnic valves.        
The valve can therefore result in substantial additional value in a drive system due to its construction-related advantages in contrast to the valves currently used in space travel applications, in particular at the end of the mission for passivation of a satellite drive system.